1. Field of the Invention
This invention relates to concrete marine floats, and more particularly, to a concrete marine float which maintains a high degree of strength while using a relatively little amount of standard, non energy intensive aggregate concrete.
2. Description of the Prior Art
Concrete floats composed of a concrete shell surrounding either a hollow or buoyant foam core have long been used in the construction of floating marine piers. These floats are generally of two different varieties. The first variety is formed with lightweight aggregate concrete utilizing thermally expanded shale in order to maximize the buoyancy of the float. The primary disadvantage of utilizing lightweight aggregate concrete is its relatively high expense. Lightweight expanded shale aggregate is normally manmade in a thermal reaction and its manufacture is extremely energy intensive. Thus, its cost has rapidly increased with the rapid increase in the cost of energy. It is conceivable that, with the possibility that fossil fuel based energy could become allocatable by end-use importance to national or regional goals, sufficient energy may not be available to the lightweight aggregate producing industry.
The second variety of concrete float utilizes naturally occurring, standard weight aggregate concrete which is substantially denser than expanded shale concrete but is much less expensive due to its lack of energy-related costs. Also, because the aggregate itself is denser, relatively less cement (another energy intensive product) need be used to achieve equivalent strength. In order to compensate for the added concrete weight while providing sufficient freeboard, the depth of the concrete float must be increased beyond the float depth or height required for floats constructed of expanded shale concrete. The additional depth further adds to the weight and displacement of the float thereby aggravating the need for additional buoyancy which is provided by an even deeper float. As a result, standard weight aggregate concrete floats are proportionately larger and heavier than expanded shale concrete floats and the freight cost of shipping them to job sites is commensurately greater.
Attempts have been made to solve the above described problems with standard weight aggregate concrete floats by reducing the weight of such floats, generally by reducing the thickness of the concrete shell. However, with no structural support under the deck, as with an open or hollow core float, decks must have a minimum thickness of two inches to support loads typically imposed on the decks as required by building codes. Attempts have been made to utilize foam cores to support the float deck in order to allow a deck having a thickness of less than two inches. However, the foam shrinks in size with the passage of time at a far greater rate than the concrete shrinkage so that a void is soon created between the upper surface of the foam and the lower surface of the concrete deck. Consequently, even with floats having a buoyant core, the deck must be at least two inches thick.